Gettering for discharge tubes



Sept. 13, 1949. c. F. VEENEMANS ET Al. 2,482,043

GETTERING FOR DISCHARGE TUBES Filed May 14, 1946 AT TO/P/VE Y.

Patented Sept. 133 1949 f Cornelis-Frederikveenemans. and Hugo.` Ychristi'aan `.Ham'alcen Eindhovem Netherlands, ias- Conn., as trusteesignora.' by mesne assignments,` to Hartford National 4Bank and Trust Company, Hartford,

ApplicationrMay 14, 1946, serial-N6. 669,513

Inuthe Netherlands May 2, 1942i 1 sectiony 1, PubucLaw 690,Augnsts.'1'9`4e Patent expires May 2,' 1962,

In connection with VVelectric discharge tubes it has for a long` time.`been. aproblem toV arrange for the optimum emissionaoflkan oxide cathode arranged iternally'ofthe tube; that is to say a cathode Whose emitting -layer is formed by one or more oxides ofA the alkaline or alkaline ear-thi metals, which `oxides-are generally developed by the application anddecomposition of the carbonate of hydroxide. It is known to use, in thesetubesl-gas-combining-substances or getters; by which harmful. gases or vapours developingin :the tubepwhilelit is: in use or inthe last stage Vof theMmanufacture can be taken up. Exhaustive experiments Y hayebeen under-taken by the applicants in connection with the presence of various gases or vapours in these tubes and the eiect thereby produced on the oxide cathode. It has thus been revealed that one of the constituents most harmful to the cathode is chlorine and that this element either free or combined is developed in appreciable quantities in the tube and it is not absorbed by the getter, at least not to a sufllcient extent. As revealed by various experiments, it is not improbable that the source of this chlorine is to be seen in the presence of chlorine compounds. particularly of chlorides, in the glass of the tube wall and that the harmful action occurs during the manufacture of the tube. Upon heating of the Wall, for example during the deprivation of gases, this chloride -may indeed be transformed in the following rnanner:

the hydrochloric acid vaporising from the wall and, jointly with undecomposed barium carbonate which isv already present on the cathode,

Y forming The barium chloride formed leaves the cathode by evaporation during the decomposition of the carbonate and deposits on the anode. Whenthe cathode is formed, this barium chloride is decomposed by the bombardment of electrons during which chlorine contacts with the active barium on the cathode, with the result that barium chloride is again produced, which again may escape by evaporation to the anode and so forth; the cathode is poisoned by this process. Now, it might be imagined that these phenomena would not be troublesome if the tube contained substances capable of combining with chlorine or hydrochloric acid; thus, for example at a given point in the tube a getter could be arranged for these substancesby which the hydrochloricv acid developed' from the Vbulb VWall could be xed. It is njow found that these means arefnot effective or at' least' are insufficiently effective and that theus'e thereof does not permit or avoiding theV reactionhereinbeiore de,- scribed between the hydrochloric acidand the bariumcarbonate, this being duejto the fact that the carbonate itself acts as a hydrochloric acid getter. Now, these diiiculties can` b'e obviated by the use of'a discharge tube 'according tothe invention. lnfsuch atubewhose wall is at least `partially of glass and which comprises anlelectrode system including an oxide cathode the-inside of the glass Wall hasappliedto'it a substance Which combines with chlorine' and the fact that these compounds are xed directly near the point at which they are developed; ob-

viously, the substance applied has to be chosen Y in such manner that other products detrimental to the emission of the cathode are not produced.

For this purpose, the wal1 hasV appliedrto it such substances that if upon reaction with chlorine-containing compounds volatile products are evolved these products do not produce any harmful effect on the emission of the cathode and particularly do not react with the undecomposed alkaline earth salt Which during the removal of gases from the bulb is already present on the cathode. The term volatile products is to be understood to mean the normal gases and vapours that develope during the removal of gases and are to be removed by pumping, such Vas vapour, carbonio acid, hydrogen and carbon oxide.

Suitable substances and groups of substances capable of being applied to the Wall for the purpose here described are, for example, basic oxides, such as Vcalcium oxide, zinc oxide and similar hydroxides, for example potassium or sodium hydroxide, salts, particularly carbonates and some metals, such as zinc, lead and so forth. Particularly good results are obtained by the use of a thin layer of potassium or sodium hydroxide.

Since in this case it is necessary that the chlorine-containing substances evolved by all parts of the glass wall should be combined immediately-it is highly desirable that the Whole surface of these glass component members or at least the greater part thereof should be coatedy on the inside with a thin layer of the active substance. It is obvious that the substance applied has also to'beV chosen in such manner that at the temperatures occurring on the inside of the glass wall, which generally are not in excess of 300 to 350 C., harmful gases or vapours are noti formed.

A layer of a substance according to the'inven'- tion may be obtained in thepfollowing manner. Before the bulb of a discharge tube is placed on the stem a thin layer of potassium hydroxide is.

tube the bulb wall is then heated in Vorder toV remove the occluded gases the hydrochloric acid thus evolved is fixed by r the potassium hydroxide with the production ofp'otassium chloride, which is not decomposed or `vaporised at the temperature prevailingjat these points and of vapour, which escapes and is. pumped off. After the removal of gases from the various wall parts and the electrodes itis'p-ossible, without any risk of poisoning the cathode; to' decompose the carbonate' .present thereon to form oxide, it being then possible to nish the tube in the normal manner.

An electron discharge tube in accordance with the invention is Vshown in the drawing in which a glass envelope containing an anode and anV oxide cathode has the inner surface thereof provided with a gettering substance capable of chlorine xation. Y

We claim:

1. An electron discharge tube comprising an envelope enclosing an evacuated l.space and having glassswall: portions',l .and a layer -of a gettering substance capable of chlorine fixation on subjstantially the entire inner surface of said glass wall portions,

- envelopev enclosing-- an evacuated space and hav' f2'."An electron'discharge tube comprising an ing glass Wall portions, and a layer on substanv tially-the entire sinner surface of said glass wall Y portions o'f a getterfing substance capable of chlorine-fixation comprising a material chosen from I the grouponsisting of potassium Vhydroxide and sodium hydroxide.

3. An electron discharge tube comprising an envelope enclosing an evacuated space and hav- `Ving glass wall portions, a layer on substantially the entire inner surface of said glass wall portions REFERENCES CITED The following references are of record in the le of this patent:

y'UNITED {s'rA'rE's PATENTS NumberA f Name- Date 1,552,128 Ettinger et al Sept. 1,1925 1,552,310 Kayko 1 Sept. 1, 1925 

